Steinbeck wrote 'Flight'? I think you might be mixing up the author. The short story 'Flight' is by John Steinbeck, it's in his collection 'The Long Valley'. It's not a novel, so there isn't a sprawling main plot in that sense. It's a tight, brutal tale about a young man, Pepé, from a poor Californian family who gets into a knife fight and has to flee into the mountains. The plot is essentially his desperate, doomed attempt to escape the men tracking him. It's less about the chase itself and more about watching a boy unravel under isolation and terror, slowly losing his possessions, his sanity, and finally his life. Steinbeck paints the landscape as this unforgiving character that grinds him down.
I read it years ago for a class and the imagery of Pepé's gradual degradation—the loss of his hat, his water, his horse—stuck with me more than any complex plot twist. The climax is stark and inevitable. It feels like a Greek tragedy set in the California hills, a study of fate and man's powerlessness against nature and consequence. The main 'plot' is just the process of dying.